Needle-free delivery of a liquid drug can be achieved by pressurizing the drug and rapidly ejecting it through a narrow orifice, thereby creating a high speed jet which can readily penetrate skin and the underlying tissue. Typically, this technique requires a pressure of 10 to 60 MPa to be developed on the drug over a few milliseconds, and then maintained for up to 100 ms.
Needle-free drug delivery has several advantages over needle-based delivery, particularly when many successive injections are required or injection discomfort is a major concern. However, in order for needle-free injector devices to become ubiquitous, they need to be controllable, repeatable, portable, and inexpensive.
Until very recently, most of the portable devices developed for jet injection have relied on springs or compressed gases to store and then rapidly release energy in order to create the high pressures required. The use of shape memory alloys and magnetic drives has also been proposed for actuating in jet injectors.